Jan Hušek

Cyclicity and variability in prey dynamics strengthens predator numerical response: the effects of vole fluctuations on white stork productivity

Theory predicts that optimality of life-long investment in reproduction is, among other factors, driven by the variability and predictability of the resources. Similarly, during the breeding season, single resource pulses characterized by short periods and high amplitudes enable strong numerical responses in their consumers. However, it is less well established how spatio-temporal dynamics in resource supplies influence the spatio-temporal variation of consumer reproduction. We used the common vole (Microtus arvalis)—white stork (Ciconia ciconia) resource—consumer model system to test the effect of increased temporal variation and periodicity of vole population dynamics on the strength of the local numerical response of storks. We estimated variability, cycle amplitude, and periodicity (by means of direct and delayed density dependence) in 13 Czech and Polish vole populations. Cross-correlation between annual stork productivity and vole abundance, characterizing the strength of the local numerical response of storks, increased when the vole population fluctuated more and population cycles were shorter. We further show that the onset of incubation of storks was delayed during the years of higher vole abundance. We demonstrate that high reproductive flexibility of a generalist consumer in tracking the temporal dynamics of its resource is driven by the properties of the local resource dynamics and we discuss possible mechanisms behind these patterns.

Postfledging Movements in Birds: Do Tit Families Track Environmental Phenology?

ABSTRACT. Recent research on reproduction in animals has emphasized phenology and prey matching in the long term and on large spatial scales (e.g., linked to global climate change). We studied how individuals within one reproductive cycle and at small spatial scales may try to maximize access to food resources that vary in space and time. Herbivorous mammals are known to track favorable phenological stages of their food plants and move seasonally on the landscape. Whether phenology similarly affects spatial movements of birds on their breeding grounds is largely unknown. We studied postfledging movements of Blue Tits (Cyanistes caeruleus) and Great Tits (Parus major) when the young were escorted by parents during 19 to 43 days posthatching. This was done over 4 years in a 1.6-km2 woodland area in Norway in which an elevational gradient (105–266 m) caused a phenological delay in vegetation and peak abundance of caterpillar prey at the higher elevations. Postfledging movements were similar in the two tit species, with a mean distance moved from the nest to the site of observation of 134 m (range: 6–1,036, n = 104). On average, families moved upslope (mean = 4.8 m, range: -23 to 69 m; P = 0.002, n = 104), which suggests that they were able to track environmental phenology. However, most families did not move far from the nest site, possibly because the parents tried to defend a year-round territory and, therefore, could not afford to leave for longer periods.

Natal dispersal based on past and present environmental phenology in the pied flycatcher (Ficedula hypoleuca)

Natal dispersal allows individuals to reach suitable breeding sites. The effect of present plant phenology as a cue for dispersal into areas with favourable stages of development has been well established across avian and mammalian taxa. However, the effect of past experience is less understood. We studied the effect of past and present phenology of the environment on the direction and distance of natal dispersal in a passerine bird, the pied flycatcher (Ficedula hypoleuca). We monitored spring settlement of local recruits in six nest box plots along a 10-km stretch of a south-north gradient of plant and caterpillar food development. We found that males used both past experience of caterpillar phenology from early life and actual plant phenology during the recruitment season as independent cues for breeding settlement. Males that had experienced a mismatch with the caterpillar food peak as a nestling, and/or those that arrived late in the spring in the recruitment year, moved north of their natal site, whereas males that had experienced a better match with the caterpillars as a nestling, and/or those that migrated earlier in the spring, settled at a similar site or more to the south. In females, no such effects were found, suggesting that the usage of phenological cues is sex specific. In summary, tracking environmental phenology by natal dispersal may represent an effective mechanism for settling in new favourable areas, and may thus potentially cause rapid change of a species’ geographical breeding range in response to climate change.

The effect of oilseed rape occurrence on main prey abundance and breeding success of the Common Buzzard Buteo buteo

Capsule The occurrence of oilseed rape increased main prey abundance and breeding success of Common Buzzards. Aims We tested whether the occurrence of oilseed rape influences the abundance of Common Voles, i.e. the main prey of Common Buzzards and so also nesting activity and breeding success of Common Buzzards. Methods The study was carried out in 2005–2012 in a 38 km2 area in western Poland, where oilseed rape plantations (12–106 ha) covered 18% of the agricultural land. The number of active burrow entrances was used as an index of vole abundance in various crops, and Buzzard breeding performance, i.e. the occurrence of annual nesting attempts in individual long-term nesting sites as well as the presence and number of fledglings, was estimated by observations of their nests. Results The index of vole abundance was highest in oilseed rape, and judging by the proportion of active burrow entrances (33–77%), the plantations of rape typically supported a larger portion of the local vole population than other crops. The acreage of oilseed rape fields around individual nesting sites of Buzzards did not affect the probability of nesting attempts in these sites. However, the probability of successful nesting and the number of fledglings per successful nest increased with the area of oilseed rape around the Buzzard nesting sites. Conclusion The occurrence of oilseed rape may positively affect prey availability and in turn the breeding success of Buzzards. The spread of oilseed rape may therefore also be beneficial for other vole-eating raptors hunting in the agricultural landscapes.

Impact of Nesting Mortality on Avian Breeding Phenology: A Case Study on the Red-Backed Shrike (Lanius collurio)

The seasonal timing of avian reproduction is supposed primarily to coincide with favourable feeding conditions. Long-term changes in avian breeding phenology are thus mostly scrutinized in relation to climatic factors and matching of the food supplies, while the role of nesting mortality is largely unexplored. Here we show that higher seasonal mean daily mortality rate leads to a shift in the distribution of breeding times of the successful nests to later dates in an an open-nesting passerine bird, the red-backed shrike Lanius collurio. The effect appeared to be strong enough to enhance or counteract the influence of climatic factors and breeding density on the inter-annual variation in mean hatching dates. Moreover, the seasonal distribution of reproductive output was shifted to larger, or smaller, broods early in the season when the nesting mortality increased, or decreased, respectively, during the season. We suggest that population level changes in timing of breeding caused by a general advancement of spring and of the food supplies might be altered by the seasonality in nesting mortality. Hence, we argue that consideration of nesting mortality is of major importance for understanding long-term trends in avian phenology, particularly in species capable of renesting.

Analysing Large-Scale Temporal Variability in Passerine Nest Survival Using Sparse Data: A Case Study on Red-Backed Shrike Lanius collurio

Abstract. Availability of nest survival estimates over large spatial and temporal scales is necessary for the complex modelling of population dynamics. However, there may be no standardized nest monitoring schemes, as a primary source of data, for many species, locations or years. Although other potential datasets often do exist, their applicability for analysing large-scale temporal patterns in nest survival is not well established. We used an alternative dataset of ringing records of 3 091 nests of the Red-backed Shrike Lanius collurio, representing five time series (6 to 42 years) from different sites within the Czech Republic, to analyse long-term variability in nest survival. We modelled trends in daily nest survival rates (DSR) over the years, either assuming a constant DSR, or accounting for unequal nest search efforts during the breeding season by assuming that DSR varies as a function of nest age and seasonal date. We found that even sparse nesting data may produce realistic estimates of nest survival. DSR varied greatly among sites, from 0.975 to 0.984, corresponding to a nest success from 48% to 62%. Both modelling approaches yielded almost identical estimates of DSR trends over the years. In this study, nest survival has either declined at all three agricultural sites or remained stable at one suburban site since the late 1980s. We conclude that sparse datasets with unequal searching effort during the nesting cycle and/or nesting season can be used to estimate long-term trends in nest survival, but this approach is warranted only if the analyses, based on different assumptions, yield consistent estimates.

Rapid Decline of Common Cuckoo Cuculus canorus Parasitism in Red-Backed Shrikes Lanius collurio

Several 19th and 20th century studies on Common Cuckoo Cuculus canorus brood parasitism suggest that Red-backed Shrikes Lanius collurio used to be one of its common hosts in central Europe. However, since the late 1960s parasitism ceased to occur in Red-backed Shrikes in Hungary. Using data from bird ringing records in the Czech Republic and Slovakia we evaluate whether this finding holds on a broader scale. We found a rapid decline in the parasitism rate, expressed as the frequency of Common Cuckoo chicks encountered in Red-backed Shrike nests, during 1964–2006. During the first decade of the study, on average 2.19% of Shrike nests contained a Cuckoo chick, while in the last decade Cuckoos occurred in 0.37% of the nests only. This suggests a six-fold decline over the study period. Parasitism rates showed strong regional variations which were positively related to the size of regional host populations. In addition to the high ability of Shrikes in discriminating Cuckoo eggs, as found in previous studies, we suggest that decreases in regional host population numbers might lead to host abandonment within a few decades. Whether these two factors work in tandem, or independently, remains to be answered.

Covariation between mean vole density and variability drives the numerical response of storks to vole prey

Hušek et al. (Popul Ecol 55:363–375, 2013) showed that the numerical response of storks to vole prey was stronger in regions where variability in vole density was higher. This finding is, at first sight, in contradiction with the predictions of life-history theory in stochastic environments. Since the stork productivity-vole density relationship is concave, theory predicts a negative association between the temporal variability in vole density and stork productivity. Here, we illustrate this negative effect of vole variability on stork productivity with a simple mathematical model relating expected stork productivity to vole dynamics. When comparing model simulations to the observed mean density and variability of thirteen Czech and Polish vole populations, we find that the observed positive effect of vole variability on stork numerical response is most likely due to an unusual positive correlation between mean and variability of vole density.

Test of Precipitation, Compensation and Monday Effect Hypotheses on Group Hare Trapping Effort

Live trapping in combination with translocation of wild animals is an important tool in wildlife management, but drivers of human trapping activity are poorly understood. Here we test three hypotheses that have been proposed to describe and explain temporal variation in group hunting-trapping effort. Namely, we test the precipitation effect, effort compensation and Monday effect hypotheses on live trapping effort of brown hares for restocking. Analysis of 26 047 hares trapped in 460 trapping days during the period 1966–1995 in western Poland showed that seasonal onset of trapping was later during rainy autumns supporting avoidance of rainy weather by the trapping group. The hunting group increased the number of animals caught the day following a day with low off-take providing evidence for the ability to respond quickly and compensate for short term variation in the trapping effort. Group trapping effort as reflected by number of hares caught was lower on Monday than on any other working day. This is in line with observations on weekly variation in working effort of employees across various contexts. We conclude that even seemingly standardized and rigid trapping schemes may be responsive to factors such as weather, experienced effort and subtle seasonal effects.